This application relates generally to the field of pulse or digital communications. Specifically, embodiments of this application relate to using suspend and active states of a Universal Serial Bus (USB)-compatible integrated circuit to communicate through the integrated circuit. Also specifically, embodiments of this application relate to using digital-to-analog (D/A) converters to communicate through a USB-compatible integrated circuit having analog-to-digital (A/D) converters.
Universal Serial Bus (USB) is a serial bus standard which allows devices to communicate to a host computer. USB is standardized by the USB Implementers Forum which is composed of computer, electronics, software, and related companies. The term USB refers to any of the revisions of the USB standard, including the popular USB 1.1 and 2.0 specifications, as well as communication buses complying with the specifications. USB also describes devices, adaptors, interfaces, and other circuits which are compatible with, but not necessarily certified as compliant with, any of the USB standards.
Other bus standards are also prevalent, such as IEEE 1394 (branded by such names as FireWire, i.LINK, and Lynx), HP-IL, RS-232, ATA, PCI, etc.; however, for simplicity and clarity this application will describe USB technologies in exemplary embodiments.
A plethora of integrated circuits exist which incorporate a USB interface. An integrated circuit (IC) is commonly known as a “chip” by the general public. An example of an IC which incorporates a USB interface is the Asahi Kasei Microsystems Co., Ltd AK5371 2-channel analog-to-digital converter with USB interface IC. The AK5371 series of chips are Certified USB™ as complying with USB Specification Rev. 1.1 and USB Device Class Definition for Audio Devices, Rev. 1.0. Another example is the BTM-CSR-FM8-C2 Bluetooth module IC provided by Perseus Technology International Corp. A wide variety of USB-compatible chips are offered for different functions and industries.
Manufacturers often purchase ICs in lots of thousands or tens of thousands in order to achieve volume discount pricing as well as establish continuity in their supply chain. The ICs are incorporated into the manufacturers' product lines over the course of months and sometimes years. Such product lines can include laptop computers, handheld PCs, printers, scanners, digital cameras, wireless keyboards and mice, automobile kits, headphones, and other industrial and consumer electronic gadgets and appliances.
As manufacturers come up with additional features to add to their products, backward compatibility with the subcomponents (e.g., ICs) within those products can be important. Consumers have come to expect backward compatibility for various devices, and industrial customers sometimes demand that future products be backward compatible before investing in a product line.
In video game systems, for example, communication between a video game console and a game input controller (e.g., controller, remote control, web camera, headset, keyboard, joystick, keypad, steering wheel and pedal, karaoke microphone, guitar, dance pad) can be accomplished through USB or other interface standards. Regardless of the interface standard, messages and message formats across the interface are predefined. Sometimes, the messages are defined well in advance of product release so that a team designing the console can prepare in relative isolation from a team designing the game input controller. Teams designing subsequent game controllers strive to meet the interface standards, sometimes running into difficulty in adding new features because the message formats do not have categories or room for the additional features.
After devices such as video game systems are released into the market, it is sometimes imperative for backward compatibility that no additional messages be added to the defined interface. For example, for a new wireless microphone, no additional messages across the serial USB interface may be added so that the new wireless microphone is compatible with the game which originally was sold with wired microphones.
In other devices, there may instead be a desire to obtain or provide additional communication functionality using a fixed standard. For example, designers of a backward-compatible webcam with fixed messages may wish to add a camera flash capability for which there are no messages. As another example, designers of a modem may wish to add encryption which is outside the normal message stream. As another example, a flashdrive designer may wish to add copy protection outside the previously defined messages.